New highly efficient radical photoinitiators based on si-si bond cleavage

Two Si-Si bond based photoinitiators that differ by their methyl versus phenyl substituents, were investigated to measure the reactivity of the silyl radicals. The Si-Si based structures, (10,10'-bis-(10-phenyl-10H-phenoxasilin) PI-1 and 9,9' -dimethyl-9,9' -bis-(9H-9-silafluorene) PI-2) were selected and through steady-state experiments, laser flash photolysis and quantum mechanical calculations. The photopolymerization ability of these photoinitiators was evaluated and compared to type I photoinitiator DMPA. Along with this the reactivity of the silyl radicals was also investigated and a mechanism for the initiation step was proposed. Nanosecond laser flash photolysis (LFP) experiments were done using Q-switched nanosecond Nd/YAG laser. As a result it was found that the reactivity of these new photoinitiators was higher than that of DMPA and they have promising potential which can increase further.